1. Field of the Invention
The present invention is broadly concerned with improved, tapered barrel twin shaft preconditioners, which are of economical design while nonetheless providing substantial preconditioning of animal feed or human food materials in order to moisturize and partially cook such materials prior to downstream processing, e.g., extrusion or pelleting. More particularly, the invention is concerned with such preconditioners having an elongated tapered barrel presenting side-by-side communicating chambers with elongated, axially rotatable, non-parallel, relatively converging shafts within the chambers and having a plurality of outwardly extending mixing elements or beaters thereon.
2. Description of the Prior Art
The majority of feed production systems include a preconditioner serving to moisturize and sometimes partially cook the starting feed ingredients (e.g., respective quantities of protein, fat, and starch such as would be found in pet food ingredients). Such preconditioners are mated with downstream processing devices, such as pellet mills or extruders. Generally, preconditioners of this type are provided with injection ports along the length of the housings for injection of steam and/or water during processing. The combination of energy (both thermal and mechanical) may serve to partially gelatinize the material passing through the preconditioner, measured as the extent of gelatinization of the starch content, but in any event provides needed moisture for facilitating downstream processing.
The preconditioner art has evolved over a long period of time. One early type of preconditioner, known as a Wenger DC preconditioner, had a pair of side-by-side chambers of equal cross-sectional area with a corresponding shaft within each chamber, and equipped with a plurality of outwardly extending, blade-like beater elements. These types of preconditioners were capable of gelatinizing the starting ingredients to a level of perhaps 20%.
A significant improvement in preconditioners is exemplified in U.S. Pat. No. 4,752,139. These preconditioners, known as Wenger DDCs, had a housing likewise presenting side-by-side chambers, but with one chamber being of greater cross-sectional area than the other. Furthermore, the shafts were operated at different rotational speeds. These types of DDC units were capable of achieving something on the order of 30% gelatinization of the starting materials.
A more recent improvement is found in U.S. Pat. No. 7,674,492. These preconditioners were similar to the DDC models, but each shaft was equipped with a variable speed drive allowing the respective shafts to be adjusted, both in terms of rotational speed and direction of rotation, during operation of the preconditioner. This latest generation of preconditioners is commercialized by Wenger as HIP preconditioners, and these are capable of achieving 50-60% gelatinization.
An alternate approach to preconditioning apparatus is illustrated in U.S. Pat. No. 7,883,263, which discloses a single shaft preconditioner of tapered design, i.e., the housing tapers at a constant angle from the larger input end to the smaller output end. The rotatable shaft carries a number of outwardly extending beaters which are of decreasing height along the length of the housing so as to conform with the taper thereof. This preconditioner is specifically designed for less expensive, relatively low capacity extrusion or pelleting systems, but nevertheless provides a high degree of moisturization and precooking of the food or feed ingredients.
Additional prior art references include U.S. Pat. Nos. 617,983, 2,831,663, 4,775,239, 5,161,888, 5,232,280, 5,460,448, 6,129,010, 6,609,819, 6,648,501, and 7,322,738, and Japanese references JP 06055050 and JP 63151341.